Rubber Research Institute of Sri Lanka, Dartonfield, Agalawatta, LK

T. Gunathilake,

Rubber Research Institute of Sri Lanka, Dartonfield, Agalawatta, LK

A. Thewarapperuma

Rubber Research Institute of Sri Lanka, Dartonfield, Agalawatta, LK

Abstract

Rhizosphere microbes and their community structure ‘biofilm’ play a significant role in maintaining the dynamic of soil fertility. In this study, isolated bacteria and fungi from rubber root rhizosphere in red yellow podzolic soils and their biofilm structures were formulated under laboratory conditions. They were evaluated for their effectiveness on solubilization of insoluble inorganic compounds, calcium hydrogen phosphate (CaHPO4), higher grade Eppawala rock phosphate (HERP) and Eppawala rock phosphate (ERP)) in liquid medium, production of indole acetic acids (IAA) and capacity of fixing atmospheric nitrogen using acetylene reduction assay (ARA). The relationships between variables were identified using regression analysis. The solubilization of CaHPO4 in liquid medium by different bacterial strains was accompanied by a drop in pH (4.2-6.1) from an initial pH of 6.8-7.0, which followed a polynomial relationship between the pH of the medium and the amount of soluble phosphorus. The medium with HERP showed less relationship compared to CaHPO4 between the above parameters. No correlation was found between pH and the amount of P solubilized of the culture medium containing ERP. Out of 30 bacterial isolates, five isolates formed proper biofilm community structure. The biofilm solubilized significantly high amount of phosphorus in liquid medium containing CaHPO4 compared to their bacterial and fungal counterparts and was observed synergistic effect for ARA. Production of IAA of biofilm was higher than that of bacteria alone cultures. Thus the biofilm formation of rhizosphere microbes seems to be very important for improved soil fertility.